Side effects from using drugs are plentiful, but each group of drugs usually have different effects to the users. <em>Depressants</em> would cause you to move slower and to lose your sense of balance, while <em>stimulants</em> would increase your heartrate and make you more alert. <em>Hallucinogens</em> would cause you to shake a lot and be restless.
Thus, from all the available options, the answer to the blank space given is (C) hallucinogens.